Curtains in the prior art that move a curtain cloth or shade vertically by a reeling rope or a reeling drum are generally comprised of a curtain bracket, a rotation driving device mounted on the curtain bracket, and a reeling rope device or a reeling drum mounted on the curtain bracket and driven by the rotation driving device. Some of the curtains are further provided with a speed reducing device to prevent the transmission members from being damaged as a result of a rapid fall of the curtain cloth or shade. The rotation driving device of the curtains is operated either by an endless bead chain (pull rope) or by a pull rope wound inside the reeling drum to wind or release the curtain. However, when it is manipulated by the endless bead chain (pull rope), a U-shaped rope loop will be formed by the hanging endless bead chain (pull rope), and a child playing around may be strangled when the child accidentally puts his or her neck into the rope loop. Manipulation through the pull rope wound inside the reeling drum needs to draw out a section of the cord to a length the same as that of the curtain cloth or the shade. The redundant length of the rope not only affects the curtain operation but also is easily entangled, such that it is impossible to handle the curtain. In order to solve these problems, technology, disclosed in China Patent Publication No. CN101025073 was developed, of the type comprised of a box, a rotary wheel rotatably mounted in the box, a rotary shaft connected to the rotary wheel for rotating a reeling drum, and a pull rope rotary wheel rotatably connected to the rotary wheel. A spring groove is formed in the pull rope rotary wheel. A spring is provided in the spring groove with an end of the spring connected to the pull rope rotary wheel and with the other end of the spring connected to the box. One or more ball recesses are transversely formed in an axial hole of the pull rope rotary wheel for rotational connection with the rotary wheel. Annular guide channels are formed in an exterior surface of the rotary wheel. One or more recesses are formed in a lateral side of the annular guide channels and project beyond the annular guide channels. Guiding grooves are provided between the annular guide channels and the ball recesses. Balls are arranged between the annular guide channels and the ball recesses, and a pull rope is wound around the exterior surface of the pull rope rotary wheel. In operation, the pull rope is drawn to rotate the pull rope rotary wheel which simultaneously winds up the spring and drives the balls to move along the annular guide channels in the exterior surface of the rotary wheel. When the balls enter the recesses at the lateral side of the annular guide channels, the rotary wheel rotates and drives the reeling drum to release the curtain. When the pull rope reaches its end, the pull rope is released to reversely rotate the pull rope rotary wheel under the resilient force of the spring and rewind the pull rope back to the pull rope rotary wheel. During reverse rotation of the pull rope rotary wheel, the balls can only move along the annular guide channels since they cannot enter the recesses at the lateral side of the annular guide channels, such that the rotary wheel will not rotate together with the reversely rotating pull rope rotary wheel. In such a way, the curtain can be fully opened by the reeling drum through continuously drawing and releasing of the pull rope. Since only one cord is provided, the risk of strangling a playful child by the neck is avoided, providing enhanced safety. However, the rotary wheel must reversely rotate together with the reeling drum to reel the curtain onto the reeling drum. Limited by the structure, the pull rope rotary wheel usually has a relatively large diameter, and the volume of the reeling drum driving device is restricted by the environment using the curtain, such that the pull rope rotary wheel cannot conceal a long cord. Furthermore, smooth reverse rotation of the reeling drum is adversely affected, because the reversely rotating reeling drum is inevitably influenced by the resistance of the rotary wheel that rotates jointly with the reeling drum. Furthermore, such a curtain has a single function, since it only can be utilized with curtain cloths or shades of a certain type.